buildroot

rabbitmq-c: new package

[Thomas:
 - pass -DBUILD_TOOLS_DOCS=OFF in <pkg>_CONF_OPTS
 - use -DBUILD_SHARED_LIBS and -DBUILD_STATIC_LIBS to enable/disable
   the creation of shared/static libraries depending on the
   configuration.
 - remove trailing spaces.]

Signed-off-by: Joris Lijssens <joris.lijssens@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>